Catastrophe
And in order to get a chicken, it would have to come from an egg of some sort? If you believed in evolution there's a slight chance that the chicken was mutated and or a smaller version of what it was back in the day, so a form of chicken would have came from an egg at some point, but in order to lay that there had to be another chicken.. and he wouldn't have gotten there without the egg, so the answer is the egg ;D ;p